A process for preparing trichloroethylene from perchloroethylene and hydrogen in which a catalyst consisting of an active charcoal support impregnated with copper in elemental or chemically bonded form and palladium, rhodium or ruthenium, in each case in elemental or chemically bonded form, is employed, is known from DE-A 2,819,209 (EP-B 5,263). The high temperatures which are required to obtain satisfactory conversion rates are a disadvantage of this procedure.
To increase the catalyst activity at a lower reaction temperature, DE-A 3,804,265 proposes the use of copper/rhodium catalysts impregnated with phosphines or phosphites. The fact that, in an expensive two-stage process for impregnation of the catalyst support, the aqueous solution of the copper compound and rhodium compound first has to be applied, and in the following step the phosphines or phosphites dissolved in organic solvents have to be applied is a disadvantage of this procedure. Above all, however, the increase in catalyst activity is limited with respect to time, so that the drop in activity after operating times of less than only 1000 hours must be counteracted by an increase in the operating temperature.
The object of the present invention was thus to provide a process for the preparation of trichloroethylene from perchloroethylene and hydrogen, with which high conversions can be achieved even at a relatively low operating temperature, even over long operating times.